Earth is under threat of global warming and resulting climate change is threatening the population with frequent or massive storms, wild fires, submerging of lands under water, and melting of useful water sources. Global warming is believed to be caused by carbon dioxide (CO2) emission from fossil fuel burning with which more than 60% of world's energy is produced. New sources of non-CO2-emissive energy, green energy, or renewable energy is constantly being pursued in order to protect the environment. Wind energy, hydro energy, and nuclear energy are examples of renewable energy sources that are being pursued.
Water shortage is also a challenging problem, not only due to global warming, but also due to dry weather in certain regions, such as California or Africa. Efficient recycling of used or polluted water will help to solve problems of shortage of water. Chemical treatment of used or polluted water, however, has been known to cause skin irritation, for example when used in swimming pools. Furthermore, such treated water often has an unpleasant odor, for example when used for drinking water. Ozone water treatment has been known as a superior water treatment process but suffers from a high energy cost of ozone production.
Luminous efficiency of lightning systems has increased, from 2% for light bulbs to 20% for fluorescent lamps or light emitting diodes (LEDs). Recent development and cost reduction of LED technology has replaced conventional light bulbs or fluorescent lamps. However, still higher energy efficiency is sought. Furthermore, LEDs are currently manufactured with a toxic chemical epitaxy growth process that is not desirable. The small size of LED is also not suitable for broad area lighting that can give the same total light output with a weak broad area emission. This broad area emission is particularly useful for preventing unintentional blinding in the eyes of people during intense small area emission.